Injections of the GABA agonist muscimol into the globus pallidus contralateral to a 6-OHDA medial forebrain bundle lesion inhibited ipsilateral rotational behavior in rats injected with both amphetamine and MK-801. These findings suggest that both stimulants are exerting their motoric effects by inhibiting GABA transmission in the globus pallidus. Injections of low doses of MK-801 to rats decreased acetylcholine levels in the striatum of freely moving rats, at the same time increasing locomotor output. These findings support the possibility that acetylcholine interneurons in the striatum may be under glutamatergic regulation.